The Theory of Signal Detectability (TSD) is a branch of information
theory devised to handle problems in the study of communication
between information sources and receivers over noisy channels. The
user of a criminological prediction device faces a similar problem in
having to make decisions, with associated costs and pay-offs, from
uncertain evidence.
This application of signal detection theory in the criminological
context is discussed with particular reference to (a) the well known base
rate problems in prediction studies; (b) the problem of finding indices of
predictive power which are independent of the base rate; (c) the various
implications and uses of the Receiver Operating Characteristic (ROC)
curve in evaluating prediction devices. These properties are illustrated
by reference to an example taken from research into the area of juvenile
offending.
